Phytochemical Composition and Antioxidant Activity of Various Grain Amaranth Cultivars

This study quantified differences in methanolic extracts composition among four grain amaranth cultivars (e.g. ‘Hopy Red Dye’, ‘Amont’, ‘Plenitude’, and ‘Golden Giant’) farmed under three planting conditions: no irrigation/no fertilization (NN), no irrigation/fertilization (NF), irrigation/no fertilization (IN). The study main outcomes were total flavonoids, polyphenols, antioxidant activity, and protein content. Antioxidant activity was assessed using two Single Electron Transfer (SET) based assays: the 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) radical cation decolorization assay (ABTS) and cupric reducing antioxidant capacity (CUPRAC). The total protein content was assessed by Gornall spectrophotometric method, the total flavonoid content (TFC) was determined using a colorimetric technique, while total polyphenols content (TPC) was assessed using the Folin-Ciocalteu method. Mean differences in outcomes were calculated using ANOVA and Dunnet’s test for multiple comparisons. The findings revealed that TPC ranged from 5 to 18 mg gallic acid equivalents (GAE)/100 g dry weight (DW), being highest in ‘Plenitude’ under NF conditions. The highest TFC (7.5 mg quercetin equivalent (QE)/100 g DW) and the highest protein content (37.25%) were revealed for the ‘Hopi Red Dye’ cultivar under the NF planting conditions. Amaranth seeds represent a potential rich source of polyphenols and protein gluten-free compounds, with the ‘Hopi Red Dye’ representing the richest cultivar in such compounds. Fertilized and non-irrigated soil provided the optimal planting conditions across all amaranth cultivars.